1. Field of the Invention
This invention relates generally to a system and method for determining the position and velocity of a plurality of vehicles relative to a host vehicle and, more particularly, to a system and method for determining the position and velocity of a plurality of vehicles relative to a host vehicle using GPS signals, where the system calculates optimal baselines between the vehicles.
2. Discussion of the Related Art
Short-baseline precise relative positioning of multiple vehicles has numerous civilian applications. By using relative GPS signals in real-time, a vehicle can establish a sub-decimeter level accuracy of relative positions and velocities of surrounding vehicles (vehicle-to-vehicle object map) that are equipped with a GPS receiver and a data communication channel, such as a dedicated short range communications (DSRC) channel. This cooperative safety system can provide position and velocity information in the same way as a radar system.
For precise relative positioning, a vehicle needs to broadcast its raw GPS data, such as code range, carrier phase and Doppler measurements. The bandwidth required to do this will be an issue in a crowded traffic scenario where a large number of vehicles are involved.
Data format defined in The Radio Technical Commission for Maritime Service Special Committee 104 (RTCM SC104) contains unwanted redundancy. For example, message type #1 (L1C/A code phase correction) uniformly quantizes corrections with a 0.02 meter resolution. The pseudo-range measurements are thus represented in a range of ±0.2×215 meters. However, the pseudo-range measurements are generally limited to about ±15 meters. It is thus noted that excess bandwidth wastage occurs if the RTCM protocol is directly used in a cooperative safety system.